The Hauerwas Eccentric
| These Hauerwas-Machines are equipped with an eccentric | |
| Transportable Machines | Stationary Machines |
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Diagrams above show grinding patterns of the Movema III-N or Taumelus III-N for different eccentric settings. The grinding pattern is produced as a hypocycloid as a result of the machining spindle and the eccentric working in opposite directions. A constant speed ratio between the spindle and the eccentric has the effect that, with one revolution of the spindle, the bases of the hypocycloid repeat themselves every 45°, also, the track of the grinding or lapping grain advances so that after one revolution of the working disc the finishing point of the curved track lies next to the starting point. The desired distribution and the slight advance can be detected clearly. They vary from one another by different settings of the eccentric and the distance from the lapping or grinding centre.
Why the oscillatory method of working?
As an example, consider a sealing surface of 200 mm,
external diameter 232 mm, circumference 728 mm
internal diameter 200 mm, circumference 628 mm
Width of sealing surface 16 mm
= Difference in circumference 100 mm
With 100 revolutions of a finishing wheel and without oscillation, the grinding or lapping disc travels a track of 10 m more on the outer diameter of the sealing surface at the same time resulting in higher cutting speed on the outer diameter. These higher cutting speeds during pure turning motion result in different material removal, depending on the applied working pressures and the material of the sealing, the sealing surfaces slope outwards and inwards. As a result of the continuously adjustable oscillation width, an additional sideways disc motion arises. By this means, the differing cutting speeds are neutralized.
The greater the eccentric is set, the greater is the oscillatory track. In this way, the detrimental difference in circumference is compensated, the duration of the reseating operation is reduced and flatness of the sealing surfaces is achieved.
The following advantages arise from the continuously adjustable oscillation width:
+ flat sealing surfaces (even without troublesome trials with different working pressures)
+ maximum space within a valve can be used for eccentric operation
+ good self - cleaning of the machine discs (this also results in greater life of the grinding sheets)
+ constantly recrossing machining marks
+ an even distribution of the paste during the lapping process
+ an additional rotating table for grinding and finest lapping of safety valves is not needed